/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */
package com.nulldev.util.data.Arrays.queues;

import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.LongAdder;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;

/**
 * An optionally-bounded {@linkplain BlockingDeque blocking deque} based on
 * linked nodes.
 *
 * <p>
 * The optional capacity bound constructor argument serves as a way to prevent
 * excessive expansion. The capacity, if unspecified, is equal to
 * {@link Integer#MAX_VALUE}. Linked nodes are dynamically created upon each
 * insertion unless this would bring the deque above capacity.
 *
 * <p>
 * Most operations run in constant time (ignoring time spent blocking).
 * Exceptions include {@link #remove(Object) remove},
 * {@link #removeFirstOccurrence removeFirstOccurrence},
 * {@link #removeLastOccurrence removeLastOccurrence}, {@link #contains
 * contains}, {@link #iterator iterator.remove()}, and the bulk operations, all
 * of which run in linear time.
 *
 * <p>
 * This class and its iterator implement all of the <em>optional</em> methods of
 * the {@link Collection} and {@link Iterator} interfaces.
 *
 * <p>
 * This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> Java
 * Collections Framework</a>.
 *
 * @since 1.6
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public class EnhancedLinkedBlockingDeque<E> extends AbstractQueue<E> implements BlockingDeque<E>, java.io.Serializable, EnhancedQueue {

	/*
	 * Implemented as a simple doubly-linked list protected by a single lock and
	 * using conditions to manage blocking.
	 *
	 * To implement weakly consistent iterators, it appears we need to keep all
	 * Nodes GC-reachable from a predecessor dequeued Node. That would cause two
	 * problems: - allow a rogue Iterator to cause unbounded memory retention -
	 * cause cross-generational linking of old Nodes to new Nodes if a Node was
	 * tenured while live, which generational GCs have a hard time dealing with,
	 * causing repeated major collections. However, only non-deleted Nodes need to
	 * be reachable from dequeued Nodes, and reachability does not necessarily have
	 * to be of the kind understood by the GC. We use the trick of linking a Node
	 * that has just been dequeued to itself. Such a self-link implicitly means to
	 * jump to "first" (for next links) or "last" (for prev links).
	 */

	/*
	 * We have "diamond" multiple interface/abstract class inheritance here, and
	 * that introduces ambiguities. Often we want the BlockingDeque javadoc combined
	 * with the AbstractQueue implementation, so a lot of method specs are
	 * duplicated here.
	 */

	private static final long serialVersionUID = -387911632671998427L;

	/** Doubly-linked list node class */
	static final class Node<E> {
		/**
		 * The item, or null if this node has been removed.
		 */
		E item;

		/**
		 * One of: - the real predecessor Node - this Node, meaning the predecessor is
		 * tail - null, meaning there is no predecessor
		 */
		Node<E> prev;

		/**
		 * One of: - the real successor Node - this Node, meaning the successor is head
		 * - null, meaning there is no successor
		 */
		Node<E> next;

		Node(E x) {
			item = x;
		}
	}

	/**
	 * Pointer to first node. Invariant: (first == null && last == null) ||
	 * (first.prev == null && first.item != null)
	 */
	transient Node<E> first;

	/**
	 * Pointer to last node. Invariant: (first == null && last == null) ||
	 * (last.next == null && last.item != null)
	 */
	transient Node<E> last;

	/** Number of items in the deque */
//    private transient int count;
	private final LongAdder count = new LongAdder();

	/** Maximum number of items in the deque */
	private final int capacity;

	/** Main lock guarding all access */
	final ReentrantLock lock = new ReentrantLock(false);

	/** Condition for waiting takes */
	private final Condition notEmpty = lock.newCondition();

	/** Condition for waiting puts */
	private final Condition notFull = lock.newCondition();

	/**
	 * Creates a {@code LinkedBlockingDeque} with a capacity of
	 * {@link Integer#MAX_VALUE}.
	 */
	public EnhancedLinkedBlockingDeque() {
		this(Integer.MAX_VALUE);
	}

	/**
	 * Creates a {@code LinkedBlockingDeque} with the given (fixed) capacity.
	 *
	 * @param capacity the capacity of this deque
	 * @throws IllegalArgumentException if {@code capacity} is less than 1
	 */
	public EnhancedLinkedBlockingDeque(int capacity) {
		if (capacity <= 0)
			throw new IllegalArgumentException();
		this.capacity = capacity;
	}

	/**
	 * Creates a {@code LinkedBlockingDeque} with a capacity of
	 * {@link Integer#MAX_VALUE}, initially containing the elements of the given
	 * collection, added in traversal order of the collection's iterator.
	 *
	 * @param c the collection of elements to initially contain
	 * @throws NullPointerException if the specified collection or any of its
	 *                              elements are null
	 */
	public EnhancedLinkedBlockingDeque(Collection<? extends E> c) {
		this(Integer.MAX_VALUE);
		final ReentrantLock lock = this.lock;
		lock.lock(); // Never contended, but necessary for visibility
		try {
			for (E e : c) {
				if (e == null)
					throw new NullPointerException();
				if (!linkLast(new Node<E>(e)))
					throw new IllegalStateException("Deque full");
			}
		} finally {
			lock.unlock();
		}
	}

	// Basic linking and unlinking operations, called only while holding lock

	/**
	 * Links node as first element, or returns false if full.
	 */
	private boolean linkFirst(Node<E> node) {
		// assert lock.isHeldByCurrentThread();
		if (count.intValue() >= capacity)
			return false;
		Node<E> f = first;
		node.next = f;
		first = node;
		if (last == null)
			last = node;
		else
			f.prev = node;
		count.increment();
		notEmpty.signal();
		return true;
	}

	/**
	 * Links node as last element, or returns false if full.
	 */
	private boolean linkLast(Node<E> node) {
		// assert lock.isHeldByCurrentThread();
		if (count.intValue() >= capacity)
			return false;
		Node<E> l = last;
		node.prev = l;
		last = node;
		if (first == null)
			first = node;
		else
			l.next = node;
		count.increment();
		notEmpty.signal();
		return true;
	}

	/**
	 * Removes and returns first element, or null if empty.
	 */
	private E unlinkFirst() {
		// assert lock.isHeldByCurrentThread();
		Node<E> f = first;
		if (f == null)
			return null;
		Node<E> n = f.next;
		E item = f.item;
		f.item = null;
		f.next = f; // help GC
		first = n;
		if (n == null)
			last = null;
		else
			n.prev = null;
		count.decrement();
		notFull.signal();
		return item;
	}

	/**
	 * Removes and returns last element, or null if empty.
	 */
	private E unlinkLast() {
		// assert lock.isHeldByCurrentThread();
		Node<E> l = last;
		if (l == null)
			return null;
		Node<E> p = l.prev;
		E item = l.item;
		l.item = null;
		l.prev = l; // help GC
		last = p;
		if (p == null)
			first = null;
		else
			p.next = null;
		count.decrement();
		notFull.signal();
		return item;
	}

	/**
	 * Unlinks x.
	 */
	void unlink(Node<E> x) {
		// assert lock.isHeldByCurrentThread();
		Node<E> p = x.prev;
		Node<E> n = x.next;
		if (p == null) {
			unlinkFirst();
		} else if (n == null) {
			unlinkLast();
		} else {
			p.next = n;
			n.prev = p;
			x.item = null;
			// Don't mess with x's links. They may still be in use by
			// an iterator.
			count.decrement();
			notFull.signal();
		}
	}

	// BlockingDeque methods

	/**
	 * @throws IllegalStateException if this deque is full
	 * @throws NullPointerException  {@inheritDoc}
	 */
	public void addFirst(E e) {
		if (!offerFirst(e))
			throw new IllegalStateException("Deque full");
	}

	/**
	 * @throws IllegalStateException if this deque is full
	 * @throws NullPointerException  {@inheritDoc}
	 */
	public void addLast(E e) {
		if (!offerLast(e))
			throw new IllegalStateException("Deque full");
	}

	/**
	 * @throws NullPointerException {@inheritDoc}
	 */
	public boolean offerFirst(E e) {
		if (e == null)
			throw new NullPointerException();
		Node<E> node = new Node<E>(e);
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			return linkFirst(node);
		} finally {
			lock.unlock();
		}
	}

	/**
	 * @throws NullPointerException {@inheritDoc}
	 */
	public boolean offerLast(E e) {
		if (e == null)
			throw new NullPointerException();
		Node<E> node = new Node<E>(e);
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			return linkLast(node);
		} finally {
			lock.unlock();
		}
	}

	/**
	 * @throws NullPointerException {@inheritDoc}
	 * @throws InterruptedException {@inheritDoc}
	 */
	public void putFirst(E e) throws InterruptedException {
		if (e == null)
			throw new NullPointerException();
		Node<E> node = new Node<E>(e);
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			while (!linkFirst(node))
				notFull.await();
		} finally {
			lock.unlock();
		}
	}

	/**
	 * @throws NullPointerException {@inheritDoc}
	 * @throws InterruptedException {@inheritDoc}
	 */
	public void putLast(E e) throws InterruptedException {
		if (e == null)
			throw new NullPointerException();
		Node<E> node = new Node<E>(e);
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			while (!linkLast(node))
				notFull.await();
		} finally {
			lock.unlock();
		}
	}

	/**
	 * @throws NullPointerException {@inheritDoc}
	 * @throws InterruptedException {@inheritDoc}
	 */
	public boolean offerFirst(E e, long timeout, TimeUnit unit) throws InterruptedException {
		if (e == null)
			throw new NullPointerException();
		Node<E> node = new Node<E>(e);
		long nanos = unit.toNanos(timeout);
		final ReentrantLock lock = this.lock;
		lock.lockInterruptibly();
		try {
			while (!linkFirst(node)) {
				if (nanos <= 0)
					return false;
				nanos = notFull.awaitNanos(nanos);
			}
			return true;
		} finally {
			lock.unlock();
		}
	}

	/**
	 * @throws NullPointerException {@inheritDoc}
	 * @throws InterruptedException {@inheritDoc}
	 */
	public boolean offerLast(E e, long timeout, TimeUnit unit) throws InterruptedException {
		if (e == null)
			throw new NullPointerException();
		Node<E> node = new Node<E>(e);
		long nanos = unit.toNanos(timeout);
		final ReentrantLock lock = this.lock;
		lock.lockInterruptibly();
		try {
			while (!linkLast(node)) {
				if (nanos <= 0)
					return false;
				nanos = notFull.awaitNanos(nanos);
			}
			return true;
		} finally {
			lock.unlock();
		}
	}

	/**
	 * @throws NoSuchElementException {@inheritDoc}
	 */
	public E removeFirst() {
		E x = pollFirst();
		if (x == null)
			throw new NoSuchElementException();
		return x;
	}

	/**
	 * @throws NoSuchElementException {@inheritDoc}
	 */
	public E removeLast() {
		E x = pollLast();
		if (x == null)
			throw new NoSuchElementException();
		return x;
	}

	public E pollFirst() {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			return unlinkFirst();
		} finally {
			lock.unlock();
		}
	}

	public E pollLast() {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			return unlinkLast();
		} finally {
			lock.unlock();
		}
	}

	public E takeFirst() throws InterruptedException {
		final ReentrantLock lock = this.lock;
		if (!lock.tryLock())
			return null;
		try {
			E x;
			if (this.count.intValue() > 0) {
				return unlinkFirst();
			}
			while ((x = unlinkFirst()) == null)
				notEmpty.await();
			return x;
		} finally {
			lock.unlock();
		}
	}

	public E takeLast() throws InterruptedException {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			E x;
			if (this.count.intValue() > 0) {
				return unlinkLast();
			}
			while ((x = unlinkLast()) == null)
				notEmpty.await();
			return x;
		} finally {
			lock.unlock();
		}
	}

	public E pollFirst(long timeout, TimeUnit unit) throws InterruptedException {
		long nanos = unit.toNanos(timeout);
		final ReentrantLock lock = this.lock;
		lock.lockInterruptibly();
		try {
			E x;
			if (this.count.intValue() > 0) {
				if ((x = unlinkFirst()) != null)
					return x;
			}
			while ((x = unlinkFirst()) == null) {
				if (nanos <= 0)
					return null;
				nanos = notEmpty.awaitNanos(nanos);
			}
			return x;
		} finally {
			lock.unlock();
		}
	}

	public E pollLast(long timeout, TimeUnit unit) throws InterruptedException {
		long nanos = unit.toNanos(timeout);
		final ReentrantLock lock = this.lock;
		lock.lockInterruptibly();
		try {
			E x;
			if (this.count.intValue() > 0) {
				if ((x = unlinkLast()) != null)
					return x;
			}
			while ((x = unlinkLast()) == null) {
				if (nanos <= 0)
					return null;
				nanos = notEmpty.awaitNanos(nanos);
			}
			return x;
		} finally {
			lock.unlock();
		}
	}

	/**
	 * @throws NoSuchElementException {@inheritDoc}
	 */
	public E getFirst() {
		E x = peekFirst();
		if (x == null)
			throw new NoSuchElementException();
		return x;
	}

	/**
	 * @throws NoSuchElementException {@inheritDoc}
	 */
	public E getLast() {
		E x = peekLast();
		if (x == null)
			throw new NoSuchElementException();
		return x;
	}

	public E peekFirst() {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			return (first == null) ? null : first.item;
		} finally {
			lock.unlock();
		}
	}

	public E peekLast() {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			return (last == null) ? null : last.item;
		} finally {
			lock.unlock();
		}
	}

	public boolean removeFirstOccurrence(Object o) {
		if (o == null)
			return false;
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			for (Node<E> p = first; p != null; p = p.next) {
				if (o.equals(p.item)) {
					unlink(p);
					return true;
				}
			}
			return false;
		} finally {
			lock.unlock();
		}
	}

	public boolean removeLastOccurrence(Object o) {
		if (o == null)
			return false;
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			for (Node<E> p = last; p != null; p = p.prev) {
				if (o.equals(p.item)) {
					unlink(p);
					return true;
				}
			}
			return false;
		} finally {
			lock.unlock();
		}
	}

	// BlockingQueue methods

	/**
	 * Inserts the specified element at the end of this deque unless it would
	 * violate capacity restrictions. When using a capacity-restricted deque, it is
	 * generally preferable to use method {@link #offer(Object) offer}.
	 *
	 * <p>
	 * This method is equivalent to {@link #addLast}.
	 *
	 * @throws IllegalStateException if this deque is full
	 * @throws NullPointerException  if the specified element is null
	 */
	public boolean add(E e) {
		addLast(e);
		return true;
	}

	/**
	 * @throws NullPointerException if the specified element is null
	 */
	public boolean offer(E e) {
		return offerLast(e);
	}

	/**
	 * @throws NullPointerException {@inheritDoc}
	 * @throws InterruptedException {@inheritDoc}
	 */
	public void put(E e) throws InterruptedException {
		putLast(e);
	}

	/**
	 * @throws NullPointerException {@inheritDoc}
	 * @throws InterruptedException {@inheritDoc}
	 */
	public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException {
		return offerLast(e, timeout, unit);
	}

	/**
	 * Retrieves and removes the head of the queue represented by this deque. This
	 * method differs from {@link #poll poll} only in that it throws an exception if
	 * this deque is empty.
	 *
	 * <p>
	 * This method is equivalent to {@link #removeFirst() removeFirst}.
	 *
	 * @return the head of the queue represented by this deque
	 * @throws NoSuchElementException if this deque is empty
	 */
	public E remove() {
		return removeFirst();
	}

	public E poll() {
		return pollFirst();
	}

	public E take() throws InterruptedException {
		return takeFirst();
	}

	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
		return pollFirst(timeout, unit);
	}

	/**
	 * Retrieves, but does not remove, the head of the queue represented by this
	 * deque. This method differs from {@link #peek peek} only in that it throws an
	 * exception if this deque is empty.
	 *
	 * <p>
	 * This method is equivalent to {@link #getFirst() getFirst}.
	 *
	 * @return the head of the queue represented by this deque
	 * @throws NoSuchElementException if this deque is empty
	 */
	public E element() {
		return getFirst();
	}

	public E peek() {
		return peekFirst();
	}

	/**
	 * Returns the number of additional elements that this deque can ideally (in the
	 * absence of memory or resource constraints) accept without blocking. This is
	 * always equal to the initial capacity of this deque less the current
	 * {@code size} of this deque.
	 *
	 * <p>
	 * Note that you <em>cannot</em> always tell if an attempt to insert an element
	 * will succeed by inspecting {@code remainingCapacity} because it may be the
	 * case that another thread is about to insert or remove an element.
	 */
	public int remainingCapacity() {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			return capacity - count.intValue();
		} finally {
			lock.unlock();
		}
	}

	/**
	 * @throws UnsupportedOperationException {@inheritDoc}
	 * @throws ClassCastException            {@inheritDoc}
	 * @throws NullPointerException          {@inheritDoc}
	 * @throws IllegalArgumentException      {@inheritDoc}
	 */
	public int drainTo(Collection<? super E> c) {
		return drainTo(c, Integer.MAX_VALUE);
	}

	/**
	 * @throws UnsupportedOperationException {@inheritDoc}
	 * @throws ClassCastException            {@inheritDoc}
	 * @throws NullPointerException          {@inheritDoc}
	 * @throws IllegalArgumentException      {@inheritDoc}
	 */
	public int drainTo(Collection<? super E> c, int maxElements) {
		if (c == null)
			throw new NullPointerException();
		if (c == this)
			throw new IllegalArgumentException();
		if (maxElements <= 0)
			return 0;
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			int n = Math.min(maxElements, count.intValue());
			for (int i = 0; i < n; i++) {
				c.add(first.item); // In this order, in case add() throws.
				unlinkFirst();
			}
			return n;
		} finally {
			lock.unlock();
		}
	}

	// Stack methods

	/**
	 * @throws IllegalStateException if this deque is full
	 * @throws NullPointerException  {@inheritDoc}
	 */
	public void push(E e) {
		addFirst(e);
	}

	/**
	 * @throws NoSuchElementException {@inheritDoc}
	 */
	public E pop() {
		return removeFirst();
	}

	// Collection methods

	/**
	 * Removes the first occurrence of the specified element from this deque. If the
	 * deque does not contain the element, it is unchanged. More formally, removes
	 * the first element {@code e} such that {@code o.equals(e)} (if such an element
	 * exists). Returns {@code true} if this deque contained the specified element
	 * (or equivalently, if this deque changed as a result of the call).
	 *
	 * <p>
	 * This method is equivalent to {@link #removeFirstOccurrence(Object)
	 * removeFirstOccurrence}.
	 *
	 * @param o element to be removed from this deque, if present
	 * @return {@code true} if this deque changed as a result of the call
	 */
	public boolean remove(Object o) {
		return removeFirstOccurrence(o);
	}

	/**
	 * Returns the number of elements in this deque.
	 *
	 * @return the number of elements in this deque
	 */
	public int size() {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			return count.intValue();
		} finally {
			lock.unlock();
		}
	}

	@Override
	public int awaitSize(final long amount, final TimeUnit unit) {
		final ReentrantLock lock = this.lock;
		try {
			if (!lock.tryLock(amount, unit))
				return this.fastSize();
			try {
				return count.intValue();
			} finally {
				lock.unlock();
			}
		} catch (InterruptedException e) {
			return this.fastSize();
		}
	}

	@Override
	public int fastSize() {
		return this.count.intValue();
	}

	/**
	 * Returns {@code true} if this deque contains the specified element. More
	 * formally, returns {@code true} if and only if this deque contains at least
	 * one element {@code e} such that {@code o.equals(e)}.
	 *
	 * @param o object to be checked for containment in this deque
	 * @return {@code true} if this deque contains the specified element
	 */
	public boolean contains(Object o) {
		if (o == null)
			return false;
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			for (Node<E> p = first; p != null; p = p.next)
				if (o.equals(p.item))
					return true;
			return false;
		} finally {
			lock.unlock();
		}
	}

	/*
	 * TODO: Add support for more efficient bulk operations.
	 *
	 * We don't want to acquire the lock for every iteration, but we also want other
	 * threads a chance to interact with the collection, especially when count is
	 * close to capacity.
	 */

//     /**
//      * Adds all of the elements in the specified collection to this
//      * queue.  Attempts to addAll of a queue to itself result in
//      * {@code IllegalArgumentException}. Further, the behavior of
//      * this operation is undefined if the specified collection is
//      * modified while the operation is in progress.
//      *
//      * @param c collection containing elements to be added to this queue
//      * @return {@code true} if this queue changed as a result of the call
//      * @throws ClassCastException            {@inheritDoc}
//      * @throws NullPointerException          {@inheritDoc}
//      * @throws IllegalArgumentException      {@inheritDoc}
//      * @throws IllegalStateException if this deque is full
//      * @see #add(Object)
//      */
//     public boolean addAll(Collection<? extends E> c) {
//         if (c == null)
//             throw new NullPointerException();
//         if (c == this)
//             throw new IllegalArgumentException();
//         final ReentrantLock lock = this.lock;
//         lock.lock();
//         try {
//             boolean modified = false;
//             for (E e : c)
//                 if (linkLast(e))
//                     modified = true;
//             return modified;
//         } finally {
//             lock.unlock();
//         }
//     }

	/**
	 * Returns an array containing all of the elements in this deque, in proper
	 * sequence (from first to last element).
	 *
	 * <p>
	 * The returned array will be "safe" in that no references to it are maintained
	 * by this deque. (In other words, this method must allocate a new array). The
	 * caller is thus free to modify the returned array.
	 *
	 * <p>
	 * This method acts as bridge between array-based and collection-based APIs.
	 *
	 * @return an array containing all of the elements in this deque
	 */
	public Object[] toArray() {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			Object[] a = new Object[count.intValue()];
			int k = 0;
			for (Node<E> p = first; p != null; p = p.next)
				a[k++] = p.item;
			return a;
		} finally {
			lock.unlock();
		}
	}

	/**
	 * Returns an array containing all of the elements in this deque, in proper
	 * sequence; the runtime type of the returned array is that of the specified
	 * array. If the deque fits in the specified array, it is returned therein.
	 * Otherwise, a new array is allocated with the runtime type of the specified
	 * array and the size of this deque.
	 *
	 * <p>
	 * If this deque fits in the specified array with room to spare (i.e., the array
	 * has more elements than this deque), the element in the array immediately
	 * following the end of the deque is set to {@code null}.
	 *
	 * <p>
	 * Like the {@link #toArray()} method, this method acts as bridge between
	 * array-based and collection-based APIs. Further, this method allows precise
	 * control over the runtime type of the output array, and may, under certain
	 * circumstances, be used to save allocation costs.
	 *
	 * <p>
	 * Suppose {@code x} is a deque known to contain only strings. The following
	 * code can be used to dump the deque into a newly allocated array of
	 * {@code String}:
	 *
	 * <pre> {@code
	 * String[] y = x.toArray(new String[0]);
	 * }</pre>
	 *
	 * Note that {@code toArray(new Object[0])} is identical in function to
	 * {@code toArray()}.
	 *
	 * @param a the array into which the elements of the deque are to be stored, if
	 *          it is big enough; otherwise, a new array of the same runtime type is
	 *          allocated for this purpose
	 * @return an array containing all of the elements in this deque
	 * @throws ArrayStoreException  if the runtime type of the specified array is
	 *                              not a supertype of the runtime type of every
	 *                              element in this deque
	 * @throws NullPointerException if the specified array is null
	 */
	@SuppressWarnings("unchecked")
	public <T> T[] toArray(T[] a) {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			if (a.length < count.intValue())
				a = (T[]) java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), count.intValue());

			int k = 0;
			for (Node<E> p = first; p != null; p = p.next)
				a[k++] = (T) p.item;
			if (a.length > k)
				a[k] = null;
			return a;
		} finally {
			lock.unlock();
		}
	}

	public String toString() {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			Node<E> p = first;
			if (p == null)
				return "[]";

			StringBuilder sb = new StringBuilder();
			sb.append('[');
			for (;;) {
				E e = p.item;
				sb.append(e == this ? "(this Collection)" : e);
				p = p.next;
				if (p == null)
					return sb.append(']').toString();
				sb.append(',').append(' ');
			}
		} finally {
			lock.unlock();
		}
	}

	/**
	 * Atomically removes all of the elements from this deque. The deque will be
	 * empty after this call returns.
	 */
	public void clear() {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			for (Node<E> f = first; f != null;) {
				f.item = null;
				Node<E> n = f.next;
				f.prev = null;
				f.next = null;
				f = n;
			}
			first = last = null;
			count.reset();
			notFull.signalAll();
		} finally {
			lock.unlock();
		}
	}

	/**
	 * Returns an iterator over the elements in this deque in proper sequence. The
	 * elements will be returned in order from first (head) to last (tail).
	 *
	 * <p>
	 * The returned iterator is <a href="package-summary.html#Weakly"><i>weakly
	 * consistent</i></a>.
	 *
	 * @return an iterator over the elements in this deque in proper sequence
	 */
	public Iterator<E> iterator() {
		return new Itr();
	}

	/**
	 * Returns an iterator over the elements in this deque in reverse sequential
	 * order. The elements will be returned in order from last (tail) to first
	 * (head).
	 *
	 * <p>
	 * The returned iterator is <a href="package-summary.html#Weakly"><i>weakly
	 * consistent</i></a>.
	 *
	 * @return an iterator over the elements in this deque in reverse order
	 */
	public Iterator<E> descendingIterator() {
		return new DescendingItr();
	}

	/**
	 * Base class for Iterators for LinkedBlockingDeque
	 */
	private abstract class AbstractItr implements Iterator<E> {
		/**
		 * The next node to return in next()
		 */
		Node<E> next;

		/**
		 * nextItem holds on to item fields because once we claim that an element exists
		 * in hasNext(), we must return item read under lock (in advance()) even if it
		 * was in the process of being removed when hasNext() was called.
		 */
		E nextItem;

		/**
		 * Node returned by most recent call to next. Needed by remove. Reset to null if
		 * this element is deleted by a call to remove.
		 */
		private Node<E> lastRet;

		abstract Node<E> firstNode();

		abstract Node<E> nextNode(Node<E> n);

		AbstractItr() {
			// set to initial position
			final ReentrantLock lock = EnhancedLinkedBlockingDeque.this.lock;
			lock.lock();
			try {
				next = firstNode();
				nextItem = (next == null) ? null : next.item;
			} finally {
				lock.unlock();
			}
		}

		/**
		 * Returns the successor node of the given non-null, but possibly previously
		 * deleted, node.
		 */
		private Node<E> succ(Node<E> n) {
			// Chains of deleted nodes ending in null or self-links
			// are possible if multiple interior nodes are removed.
			for (;;) {
				Node<E> s = nextNode(n);
				if (s == null)
					return null;
				else if (s.item != null)
					return s;
				else if (s == n)
					return firstNode();
				else
					n = s;
			}
		}

		/**
		 * Advances next.
		 */
		void advance() {
			final ReentrantLock lock = EnhancedLinkedBlockingDeque.this.lock;
			lock.lock();
			try {
				// assert next != null;
				next = succ(next);
				nextItem = (next == null) ? null : next.item;
			} finally {
				lock.unlock();
			}
		}

		public boolean hasNext() {
			return next != null;
		}

		public E next() {
			if (next == null)
				throw new NoSuchElementException();
			lastRet = next;
			E x = nextItem;
			advance();
			return x;
		}

		public void remove() {
			Node<E> n = lastRet;
			if (n == null)
				throw new IllegalStateException();
			lastRet = null;
			final ReentrantLock lock = EnhancedLinkedBlockingDeque.this.lock;
			lock.lock();
			try {
				if (n.item != null)
					unlink(n);
			} finally {
				lock.unlock();
			}
		}
	}

	/** Forward iterator */
	private class Itr extends AbstractItr {
		Node<E> firstNode() {
			return first;
		}

		Node<E> nextNode(Node<E> n) {
			return n.next;
		}
	}

	/** Descending iterator */
	private class DescendingItr extends AbstractItr {
		Node<E> firstNode() {
			return last;
		}

		Node<E> nextNode(Node<E> n) {
			return n.prev;
		}
	}

	/** A customized variant of Spliterators.IteratorSpliterator */
	static final class LBDSpliterator<E> implements Spliterator<E> {
		static final int MAX_BATCH = 1 << 25; // max batch array size;
		final EnhancedLinkedBlockingDeque<E> queue;
		Node<E> current; // current node; null until initialized
		int batch; // batch size for splits
		boolean exhausted; // true when no more nodes
		long est; // size estimate

		LBDSpliterator(EnhancedLinkedBlockingDeque<E> queue) {
			this.queue = queue;
			this.est = queue.fastSize();
		}

		public long estimateSize() {
			return est;
		}

		public Spliterator<E> trySplit() {
			Node<E> h;
			final EnhancedLinkedBlockingDeque<E> q = this.queue;
			int b = batch;
			int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1;
			if (!exhausted && ((h = current) != null || (h = q.first) != null) && h.next != null) {
				Object[] a = new Object[n];
				final ReentrantLock lock = q.lock;
				int i = 0;
				Node<E> p = current;
				lock.lock();
				try {
					if (p != null || (p = q.first) != null) {
						do {
							if ((a[i] = p.item) != null)
								++i;
						} while ((p = p.next) != null && i < n);
					}
				} finally {
					lock.unlock();
				}
				if ((current = p) == null) {
					est = 0L;
					exhausted = true;
				} else if ((est -= i) < 0L)
					est = 0L;
				if (i > 0) {
					batch = i;
					return Spliterators.spliterator(a, 0, i, Spliterator.ORDERED | Spliterator.NONNULL | Spliterator.CONCURRENT);
				}
			}
			return null;
		}

		public void forEachRemaining(Consumer<? super E> action) {
			if (action == null)
				throw new NullPointerException();
			final EnhancedLinkedBlockingDeque<E> q = this.queue;
			final ReentrantLock lock = q.lock;
			if (!exhausted) {
				exhausted = true;
				Node<E> p = current;
				do {
					E e = null;
					lock.lock();
					try {
						if (p == null)
							p = q.first;
						while (p != null) {
							e = p.item;
							p = p.next;
							if (e != null)
								break;
						}
					} finally {
						lock.unlock();
					}
					if (e != null)
						action.accept(e);
				} while (p != null);
			}
		}

		public boolean tryAdvance(Consumer<? super E> action) {
			if (action == null)
				throw new NullPointerException();
			final EnhancedLinkedBlockingDeque<E> q = this.queue;
			final ReentrantLock lock = q.lock;
			if (!exhausted) {
				E e = null;
				lock.lock();
				try {
					if (current == null)
						current = q.first;
					while (current != null) {
						e = current.item;
						current = current.next;
						if (e != null)
							break;
					}
				} finally {
					lock.unlock();
				}
				if (current == null)
					exhausted = true;
				if (e != null) {
					action.accept(e);
					return true;
				}
			}
			return false;
		}

		public int characteristics() {
			return Spliterator.ORDERED | Spliterator.NONNULL | Spliterator.CONCURRENT;
		}
	}

	/**
	 * Returns a {@link Spliterator} over the elements in this deque.
	 *
	 * <p>
	 * The returned spliterator is <a href="package-summary.html#Weakly"><i>weakly
	 * consistent</i></a>.
	 *
	 * <p>
	 * The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
	 * {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}.
	 *
	 * @implNote The {@code Spliterator} implements {@code trySplit} to permit
	 *           limited parallelism.
	 *
	 * @return a {@code Spliterator} over the elements in this deque
	 * @since 1.8
	 */
	public Spliterator<E> spliterator() {
		return new LBDSpliterator<E>(this);
	}

	/**
	 * Saves this deque to a stream (that is, serializes it).
	 *
	 * @param s the stream
	 * @throws java.io.IOException if an I/O error occurs
	 * @serialData The capacity (int), followed by elements (each an {@code Object})
	 *             in the proper order, followed by a null
	 */
	private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
		final ReentrantLock lock = this.lock;
		lock.lock();
		try {
			// Write out capacity and any hidden stuff
			s.defaultWriteObject();
			// Write out all elements in the proper order.
			for (Node<E> p = first; p != null; p = p.next)
				s.writeObject(p.item);
			// Use trailing null as sentinel
			s.writeObject(null);
		} finally {
			lock.unlock();
		}
	}

	/**
	 * Reconstitutes this deque from a stream (that is, deserializes it).
	 * 
	 * @param s the stream
	 * @throws ClassNotFoundException if the class of a serialized object could not
	 *                                be found
	 * @throws java.io.IOException    if an I/O error occurs
	 */
	private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
		s.defaultReadObject();
		count.reset();
		first = null;
		last = null;
		// Read in all elements and place in queue
		for (;;) {
			@SuppressWarnings("unchecked")
			E item = (E) s.readObject();
			if (item == null)
				break;
			add(item);
		}
	}

}
